1. Field of the Invention
The present invention relates to a plasma display panel, and particularly, a upper substrate structure of a plasma display panel (PDP) and fabricating method thereof for improving a contrast, a color temperature, and a color purity of PDP.
2. Description of the Background Art
Generally, a flat panel display apparatus can be divided into an emissive display device, and a non-emissive display device. As examples of the emissive display device, there are a field emission display (FED), a vacuum fluorescent display (VFD), an electro luminescence (EL), and the PDP, etc. In addition, as examples of the non-emissive display device, there are a liquid crystal display (LCD), and an electro chromic display (ECD), etc.
One of the most highlighted display devices is the plasma display panel (PDP). The PDP is a display device using a luminescence of visible ray which is generated by energy difference when a phosphor is excited by ultraviolet ray which is generated in plasma luminescence and returned to a base status, after injecting discharge gas in a discharge cell which is separated by a barrier rib.
The PDP can be divided into a DC type PDP and an AC type PDP according to waveform of applied driving voltage and a structure of the discharge cell. A difference between the DC type PDP and the AC type PDP is as follows.
In case of the DC type PDP, an electrode is exposed on a discharge area, and discharge current is flowed during the voltage is applied. Therefore, a resistance for restricting the current should be made on outer side. However, in case of the AC type PDP, an electrode is covered by a dielectric layer and a natural capacitive is formed to restrict the current, and the electrode is protected from a shock of ions during discharging.
Therefore, the AC type PDP which is used widely will be described in the present invention.
FIG. 1 is a cross sectional view showing a conventional PDP.
As shown therein, the conventional PDP comprises: a lower layer 2 formed on an upper part of a lower glass substrate 1; an address electrode 3 patterned on some upper part of the lower layer 2 as stripe shape; a lower substrate dielectrics 4 formed on an upper front surface of the lower layer 2 including the address electrode 3; a barrier rib 5 formed on the lower substrate dielectrics 4 for preventing a cross-talk with an adjacent discharge cell; a black top formed on an upper side of the barrier rib 5; a phosphor 6 of red, green, and blue colors formed to cover the black top, a side surface of the barrier rib 5, and the upper surface of the lower substrate dielectrics 4; a protection layer 7 disposed apart a predetermined distance from the upper side of the black top, and parallel to the lower substrate dielectrics 4; an upper substrate dielectrics 8, to which a bus electrode 9 and a sustain electrode 10 laminated with each other are inserted, formed on an upper part of the protection layer 7; and an upper glass substrate 11 formed on an upper part of the upper substrate dielectrics 8 and the sustain electrode 10. At that time, a discharge gas is filled between the upper substrate and the lower substrate. In the discharge gas, He, Ne, Ar, or mixed gas thereof is used to form buffer gas, and a small amount of Xe is used as a source of vacuum ultraviolet ray which makes the phosphor 6 be luminescent.
Operation of the conventional PDP will be described as follows.
When an electric field is applied to the address electrode 3, the bus electrode 9, and to the sustain electrode 10 to generate voltage difference between the upper and lower substrate electrodes, the discharge gas, that is, He—Ne gas or Ne—Xe gas which is formed inside the discharge cell defined by the barrier rib 5, the upper substrate and the lower substrate becomes plasma status to generate vacuum ultraviolet rays. The generated vacuum ultraviolet ray excites the phosphor 6 to generate the visible rays of red, green, or blue color. At that time, the generated visible ray is decided by the kind of phosphor 6, and accordingly, the respective discharge cell becomes a pixel representing the red, green, and blue color respectively. The visible ray is radiated outer side through the transparent upper dielectrics 8 and the upper glass substrate 11.
The upper dielectrics 8 is a layer contacting to the sustain electrode 10 using an indium tin oxide (ITO), and to the bus electrode 9 of metal electrode. And the upper dielectrics 8 uses glass of PbO type having high softening point.
Also, the upper dielectrics 8 includes Pb more than 40%, and the upper dielectrics 8 is made by applying paste in which borosilicate glass powder of 1˜2 μm diameter and an organic binder are mixed in screen printing method, and baking at the temperature of 550˜580° C.
The upper substrate dielectrics 8 fabricated as above has a dielectric constant within 10˜15 range, and a transmittance of visible ray is about 85% at peak wavelength. That is, the visible ray generated in the phosphor 6 is not radiated to outer side totally, but loss of light is generated as the light passes the protection layer 7, the upper substrate dielectrics 8, and the upper glass substrate 11. Also, the transmittance of the upper substrate dielectrics 8 is for the peak wavelength of the visible rays, and the transmittance is lowered for the wavelengths of blue and red, and therefore, the luminescent efficiency is lowered greatly.
Also, the plasma generates the visible rays generated from the discharge gas itself, and near infrared ray (NIR) adjacent to the visible ray of 0.75˜3 μm wavelength, as well as the ultraviolet rays in discharging. For example, the Ne gas which reduces the discharge voltage and makes the discharge stable is mixed with the Xe gas, that is, the discharge gas, however, the Ne gas generates the visible ray of orange color having 585 nm wavelength and generates the NIR by the discharging. In addition, a means for blocking the NIR, etc., and therefore, a color purity is lowered, a contrast is lowered, color temperature applying to the blue color mainly is reduced, and the signal of a remote controller is distorted by the NIR.